Portable power supply



FIG. 1 is a front perspective view of a portable power supply of my new design;

FIG. 2 is a side perspective view thereof;

FIG. 3 is another front perspective view thereof; and,

FIG. 4 is a rear perspective view thereof.

The broken lines in the drawings are for the purpose of illustrating portions of the portable power supply that form no part of the claimed design. 

CLAIM The ornamental design for a portable power supply, as shown and described. 